1. Field of the Invention
The present invention is concerned with article lifting or moving devices which include elongated, axially reciprocal lift posts having circumscribing guide means therearound. More particularly, it is concerned with devices of this type (such as so-called bottle jacks) which are improved by provision of anti-binding structure for preventing load-induced binding of the jack components, especially between the lift post and guide means of the jack.
2. Description of the Prior Art
Various types of jacks or article-lifting apparatus have been proposed in the past. Generally speaking, such units include an elongated, tubular axially reciprocal lifting post, along with means operatively coupled to the lift post for elevating and lowering the same as desired. Additionally, plate-type means for guiding the reciprocal travel of the lift post is a conventional feature.
One particular type of jack in use today is an air stand which is also known as a bottle jack. In such devices an air chamber having a shiftable piston therein is provided, with the lift post of the jack being secured to the piston. The upper end of the chamber is defined by an apertured guide plate through which the lift post passes. Means is also provided for filling the chamber beneath the piston with pressurized air to extend the lift post, and for release of air from the chamber to lower the lift post. The concepts of this invention may also be used with equal facility in hydraulically actuated lifting or moving devices.
A problem heretofore encountered with certain types of jacks, and particularly the so-called bottle jacks, involve load-induced binding of the jack components. For example, the lift post or ram can bind against the guide plate structure when the post is in an extended position, or the piston can bind against the chamber wall. This sort of binding most commonly occurs when an unevenly distributed load cants or deflects the jack post transversely of the longitudinal axis thereof, with the result that the post and/or piston bind against adjacent structure. This problem has been known to be so severe as to lead to rough operation, or freeze the jack and prevent post or ram movement. Furthermore, the galling of the metallic jack components incident to load-induced binding is an objectionable result.
There is therefore a need in the art for an improved jack which includes an anti-binding structure or mechanism which eliminate the problems described above.
Prior jacks and lifting apparatus are described in U.S. Pat. Nos. 2,360,735, 2,961,837, 3,087,626, 3,250,503, 3,286,970, 3,567,183 and 3,866,899.